It is well known to thermocompression bond copper leads to metallized portions of ceramic substrates. Such a technique is described in copending U.S. Patent application to B. H. Cranston, Ser. No. 546,714, filed on Oct. 28, 1983 and titled "A Lead Frame and Dual-in-Line Package Fabricated Using Said Frame", now U.S. Pat. No. 4,563,811, which is assigned to the instant assignee and is hereby incorporated by reference herein. That application discloses, inter alia, the thermocompression bonding of soft copper leads of a lead frame to metallized bonding pads on a ceramic substrate.
One known disadvantage of such thermocompressive bonding is "ceramic pullout" which may result either during bonding of the copper lead to the metallized bonding pad and/or the testing of the bond. Ceramic pullout occurs when the lead is being deformed during bonding or when a pulling force is applied to the bonded lead until a failure occurs in which the lead separates from the substrate with a portion of the ceramic substrate attached to the lead. Such ceramic pullout results in the loss of the device.
Various techniques have been tried to lessen the ceramic pullout problem. In particular, the parameters of time, temperature, pressure and materials associated with the thermocompression bonding process have been adjusted. However, such adjustments have not resulted in a solution to the problem.
Thus, there is a need for a technique to decrease the ceramic pullout failures associated with thermocompression bonding of copper leads to metallized ceramic substrates.